You can Zero an entire figure or body part without ever going to the Joint Editor.  That said, the Joint Editor is for editing joints. You use it to edit placement of joint origins, joint rotations, editing weight maps of joints, editing bulge maps of joints, and other joint related operations. If you are not creating your own character, it's rare that you would ever need this feature.

As for doing the Zero thing without using the Joint Editor, you may want to have a look at the Figure>Zero Figure menu option or Edit>Restore>Object or Edit>Restore>Figure options. 

We don't hide everything. The Zero Figure menu option does essentially what the Zero Rotations option does. It does also turn off morphs but that's a tiny thing to turn back on I would hope (I mean, I would hope whoever created your figure made morphs easy to turn back on).